1.    OBJECTIVES

 1.1        To realize Magnetic Resonance Imaging studies with T.S.E (TURBO SPIN ECO) and three-dimensional Reconstruction in prelingual patients having deep neurosensorial hypoacusia.
 
1.2        To realize Magnetic Resonance Imagenology studies with T.S.E and three-dimensional Reconstruction in those patients having normal audition that will be the control group.
 
1.3       To evaluate in the images obtained the Morphology of the cochlea - semicircular channels and vestibule, acoustic-facial package, vascular structures of the IAC ( INTERNAL AUDITORY CANAL). Morphology and dimensions of the cochlear and vestibular aqueducts.        
 
 
 

2.    PURPOSES

2.1.      To establish an imagenolic type diagnostic method that will enable us to evaluate in a more reliable way those patients having deep bilateral neurosensorial hypoacusia.
 
2.2     If possible, to look for the etiological cause, responsible for the deep neurosensorial hypoacusia in those patients whose etiology has not been determined and due to this their hypoacusia has been denominated as idiopathic.


 

3. THEORETICAL FRAMEWORK
 

Patients with otoneurologic symptoms such as progressive neurosensorial hypoacusia, tinnitus, vertigo, sudden deafness and fluctuating hypoacusia undergo many clinical, para-clinical, audiological, neurophysiological and imagenologic studies, with the purpose to obtain better diagnostics each time; however, no matter the efforts, the diagnoses we do today don’t get to the ultimate cause.
 
The study of the internal ear  is made by parts, according to its components.
 
The high resolution CT is the method of election for studying the anatomy and the alterations of bony labyrinth (2); in the functional part, we study the integrity of the neurological via and the proper functioning of the sensorial organ, through audiological and neurophysiological analyses(1,2); which suggest the location of the lesion and the affectation level of the function, without showing us the defect physically.
 
During the past decade, the development of the imagenologic techniques has enabled us to study the anatomy and the pathology of soft tissue structures in vivo, cerebellopontile angle cisterna, and in general the pathway of the auditive
 
via, using MRI. In the last two years, better technological modalities that allow us to visualize in three dimensions the membranous labyrinth, the endolymphatic and  the cochlear aqueducts, the different ramps and even the endocochlear liquids have been developed, offering a better opportunity to find and to clarify the pathology that affects the patients having symptoms such as neurosensorial hypoacusia, vertigo and tinnitus, improving the treatment possibilities. For the congenital malformation cases, lesions of the petrous apex, mixed deafnesses, or studies for cochlear implant, the MRI and the CT are complementary studies.
 
The technological modality that we used in our study was developed by General Electric in 1.994 and was denominated 3D-TSE. It uses a turbo image sequence with no echo with continued 0.7 mm or overlapped 1.5 mm cuts that enable to obtain the image of many previously invisible structures. For example,  the endolymphatic aqueduct can be visualized in 50 – 73% of the studies, always being visible in the pathologic dilatation cases (It must not have a diameter greater than 1.5 mm).
 
In 96% of the studies, the cochlear aqueduct; the trifurcation of the  vestibulocochlear nerve; the facial nerve differentiation in the IAC, the AICA (ANTEROINFERIOR CEREBELLAR ARTERY) vascular loop in the cerebellopontile angle or in the IAC; the tympanic and vestibular scales and the cochlear duct in the different rounds of the cochlea; the Reissner’s membrane;
 
the lamina spiralis; the basilar membrane; the Corti’s organ; the three semicircular channels with their ampules; and the vestibule, in which the utriculus and the saccule are confused. (7,8,10,11,13).
 
The importance of the 3D techniques is grounded in the anatomic identification of very little structures as it was stated earlier and its applications are:
 
- Congenital anomalies: They go from dysplasia to aplasia of the components, limited in some ocassions to the membranous labyrinth, with a normal CT. The cochlear hypoplasia usually may exist associated with vestibule or semicircular duct dilatation, in which the labyrinth size and permeability must be studied and the size of the cochlear nerve must be estimated.
 
Vestibular and semicircular duct dysplasias may also exist with a greater engagement of the lateral duct due to it has been considered the last embryologic structure to be made. Estenosis or IAC (INTERNAL AUDITORY CANAL) dilatation may also be seen associated with perilymphatic fistulas and it is described in the Gusher’s  syndrome (8).
 
- Trauma: MR makes objective the interval and the extension of the secondary fibrosis to the labyrinthine contusion throughout the pathway of the fracture.
 
- Bacterial labyrinthitis: They are associated with a decrease of the liquid signal  in  T2 sequences
- Cochlear preimplant assessment: The image study must predict the cochlear permeability before surgery; the dimorphic changes of the internal ear must be detected also. In this case the CT allows a chartography of the bony labyrinth and the petrous; it searches for anomalies of the round window and the membranous labyrinth calcifications showing the cochlear ossification, some labyrinth malformations and traumatic deformations. The 3D-MRI has a very important place; it shows the labyrinthine fluid much clearly and it may predict the cochlear fibrosis before the ossification, being much more sensitive to detect these types of anomalies, providing information about the state of the endolymphatic and perilymphatic liquids. Several times, alterations are not detected, mainly in those patients who have progressive idiopathic hypoacusia, ototoxicity or acute deafness (23, 24, 25).
 
- Vertiginous syndrome study: Not always the central or peripheral origin of vertigo may be identified, the first examination that the patients must go through is a study by MR that shows a central lesion ( stem, cervico-occipital junction), a peripheral cause (cerebellopontile angle, acoustic-facial pedicle) or an engaged membranous labyrinth (expansive or inflammatory). It must include all the noted sequences, the 3D-MRI and AMR (Angiography by Nuclear Magnetic Resonance) in case of vascular loops suspicion or caliber or encephalic vessel flow anomalies (26).
 
- Sudden Deafness: It has many origins. Usually, nothing is found, but it may be helpful in order to discard other alteration. (8).
 
- Pathology of the Content of the IAC: The use of T2 millimetric cuts allows the identification of neurinomas with an approximate diameter of 1 mm, which are usually asymptomatics. The usage of gadolinium in the neurinomas’ search is not justified except when looking for an inflammatory pathology of the nerve or of the concomitant labyrinth. Only 1% of the patients with neurosensorial deafness has an acoustic schwanoma, 85% of which are born in the vestibular branch, more than 95% are solitaires. In T2-TSE sequence it is present a neurinoma with a hypointense lesion throughout the nervous axis and the relationships between this and the bottom of the IAC must be studied. These TSE sequences are very precise in the diagnosis of 98% of 2mm tumors, and must be used in those patients who have unilateral symptoms such as progressive neurosensorial hypoacusis, unilateral tinnitus and sudden deafness.
 
In some very small acoustic tumors it is possible to find the nerve of origin, which has a prognostic value because the ones originated in the higher vestibular nerve have a greater possibility of preservation of audition than those that are born in the lower vestibular nerve.
 
 
- Vascular loops: In 10% of the patients, the fine cuts confirm the presence of one normal vascular loop within the IAC.
 
- Expanded endolymphatic duct and sac syndrome: It is the cause of progressive deafness during childhood or adolescence, its origin is unknown.  Endolymphatic duct expansion can be accompany by cochlear and vestibular anomalies. It is a bilateral affection in more than half of the cases and it is 100% associated with deafness, 33% with vertigo. Hypoacusis is fluctuating and may become worse with a minor trauma. It is usually discovered in adulthood so it is very important the MR study, which is superior than the CT, because it visualizes the endolymphatic duct and sac directly and it is not an indirect measurement as the bony vestibular aqueduct measurement is. (10, 28-30)
 
- Endolymphatic sac tumors: They are responsible for a labyrinthine dropsy.
 
- Meniére’s syndrome and diesase: the endolymphatic dropsy is the clinical triad of progressive and fluctuating hypoacusis, episodic vertigo and non-pulsatile constant tinnitus. The Meniére’s syndrome has an identifiable cause (e.g., syphilitic dropsy) and the disease is idiopathic. The primary cause of the volume increase of the endolymph is an unbalance between the secretion and the reabsorption of the endolymph that could possibly be secondary to a  membranous endolymphatic duct and sac obstruction located in the vestibular aqueduct. The imagenologic.

- Descriptions have conflictive reports, noting stenotic vestibular aqueducts (31), the presence of aerial cells around the vestibular aqueduct, short aqueducts and few mastoid pneumatization.
-  No really useful findings have been made until now but it must be studied in order to exclude another cause of the symptoms (2).


 

4. HYPOTHESIS

 4.1   3D–MRI enables us to determine or conclude one etiological cause of structural type in some of such patients with deep idiopathic bilateral neurosensorial hypoacusis.

4.2   3D-MRI is a complementary technique of the computed tomography, which is useful for the diagnosis of patients having deep bilateral neurosensorial hypoacusia.

 

5. MATERIALS AND METHODS
 

Sixty six persons were prospectively studied as a whole (132 internal ears), 7 subjectively healthy and 59 patients who had a neurosensorial deafness background, from the “Instituto Nuestra Señora de La Sabiduría para Niños Sordos” (Our Lady of Wisdom –  Deaf Children Institute) between the ages of 9 and 22 years, assessed by two otologists and to whom a recent audiometric study had been practiced.
 
The otologic evaluation included a complete cross-examination and an exhaustive physical exploration. The audiologic study included tone audiometry and logoaudiometry, with the purpose of establishing the type of hypoacusia present in the patient.
 
In all of them a comparative MRI study of both ears was made in a superconductive clinical image equipment  by IT (Philips Gyroscan 10-NT), with an antenna of a circular surface of an 11 cm diameter opening (C3), centered on the meatus of the external auditive channel. At first we used a T1 sequence for localization in the coronal plane followed by radio frequency turbo type pulse spin echo potentiated in T2 sequences, with fine cuts overlapped in the axial plane, whose general parameters were: Tr 9000-11000 mseg, TE 600 mseg, 40 cuts with a cut width of 1.5 translapped mm with a –1 mm interspace, FOV 130 mm, RFOV 80%, matrix of 256X256,3 acquisitions (NSA) and a total acquisition time of 6:29 minutes in each ear. All these images were photographed and analyzed separately as well as the subsequent three-dimensional reconstruction using the algorithm standard of maximum intensity projection (MIP)  of the coronal plane to the transversal plane with 15 radial images.
 
The findings were compared subsequently with the clinic and previous studies such as the CT in every case.
 
In all the studied internal ears it was analyzed the identification or not of the anatomic structures of the original images and of those rebuilt images (MIP).
 
The following parameters were evaluated during the study:
 
-     Cochlear morphology
-     Vestibule and semicircular channels morphology
-     Evaluating each one of the three channels, the presence or not of vestibular expansion.
-     Vestibular and cochlear aqueduct’ diameter.
-     Expansion or not of the endolymphatic sac
-     Acoustic-facial package morphology.
-   Vascular structure visualization of the IAC evaluating them at the acoustic pore and the cerebellopontile cistern levels.
-     IAC morphology.

6. UNIVERSE AND SAMPLE
 

Two groups of patients were chosen: A first group constituted by 7 healthy patients, who had completely normal audition, with no personal nor family hypoacusia background, average age of 20. This will be the control group.
 
The second group is made up of 59 patients with deep bilateral, acquired or detected before the age of 5, neurosensorial hypoacusia.

The age of these patients goes from 9 to 22 years.
 
The two groups of patients had made an imagenologic study in both ears.

 
7. RESULTS AND CASE PRESENTATION

The obtained results from this study must be carefully analyzed.
 
We believe that this technique has opened a window towards clarifying some of the pathologies that were unknown until now and that are very important to diagnose.
 
It is important to clarify that these 66 patients with deep bilateral neurosensorial hypoacusia had previously undergone a high resolution computed tomography and it had been reported as normal.
 
The first obtained data is the percentage of abnormal imagenologic findings by 3D-MRI in those patients having deep bilateral neurosensorial hypoacusia. Finding that 59 patients having deep neurosensorial hypoacusia, with previous CT reported as normal, the abnormal findings by 3D-MRI were in 13 patients (25 ears) which is equivalent to 22%. (Table No. 1).
 
From the 12 patients having neurosensorial hypoacusia due to meningitis, in two patients the obliteration of the membranous labyrinth is evident (4 ears) 14%, in the rest of the patients there was no alteration (Table No. 6).

 
PRESENTATION OF CLINICAL CASES

Next we present the images obtained from three patients with no pathology (photos 1,2 and 3) in which all the structures of the internal ear may be seen in great detail.
 
- A patient with bilateral malformation of the internal ears. In the right side the higher vestibular branch of the vestibulocochlear nerve may not be identified, the vestibule is small, only one of the endings of the semicircular duct may be identified. In the internal ear the IAC is stenotic, in its interior no nervous structure may be identified, the vestibule and the posterior and upper semicircular ducts are dysplasic and the lateral semicircular duct may not be identified either (photos 4 and 5).
 
- Two cases of endolymphatic duct and sac expansion syndrome in three patients. One was 10 years old and had symmetric bilateral expansion; both were men, the first one had deafness attributed to ototoxics (Kanamycin) and the second one had complete progressive right deafness and 75% in the left side (photo 6).
 
- A 22 year old patient with neurosensorial hypoacusis in whom the cochlear apex could not be seen and only one ending of the posterior semicircular channel on the engaged side was visible, having a normal CT and a normal contralateral study  (photo 7).
 
- A 6 year old girl patient who had deep congenital right deafness of unknown etiology to whom in the engaged ear we may see the stenotic IAC and the nervous branch may not be identified, with no other associated alterations and a normal left ear (photo 8).

 
8.  DISCUSSION

 
The results of the imagenologic studies in the patients with neurosensorial deafness show great variations and only in a few cases they have identifiable anomalies. The direct visualization of the soft tissues, the internal ear, and the membranous labyrinth liquids including the endolymphatic duct and sac in MRI that include 3D-TSE sequences is higher to the CT of the temporal bone which only identifies the channels of the bony labyrinth; the MRI plays a preponderant  place in the identification of the anatomy and pathologies of the membranous labyrinth and the associated neural structures, being MRI an essential complementary study to delineate the structural anomalies of the internal ear, even though, as it is described only by a low percentage (18.4% in our study) of the patients having neurological deafness show internal ear alterations, being of the membranous labyrinth associated or not to bony labyrinth malformations and vestibulecochlear nerve aplasia, a finding that counter indicates the positioning of a cochlear implant.
 
These sequences with infra-millimetric cuts potentiated in T2-TSE are also the choice for studying those patients with suspicion of the membranous labyrinth obliteration usually secondary to chronic labyrinthitis from a different etiology including luetic, viral, autoimmune as the Cogan’s syndrome; bacterial of  thympanogenic, meningogenic, hematogen or posttraumatic origin since these may predict the cochlear fibrosis before the visible ossification by CT.
 
This technique must be attached to the cochlear permeability study in the patients chosen for cochlear implant, with repercussion in the type of implant and the surgical technique that will be used.
 
It is also the chosen examination to identify and characterize those young patients with endolymphatic duct and sac expansion syndrome with hypoacusis, or unilateral or bilateral neurosensorial deafness, allowing also the identification of membranous labyrinth dysplasias that may be associated with this syndrome and displacing the CT that was the method of choice for the diagnosis of the Vestibular Aqueduct Expansion syndrome, as previously known.
 
In cases were there is a neurovascular compression suspected that usually presents with a hemifacial spasm, trigeminal neuralgia, vertigo and tinnitus with or without associated neurosensorial hypoacusis. This new T2-TSE sequence with complementary AMR are the chosen methods to establish these loops, which are described as “normal” findings in asymptomatic patients.
 
It must also be practiced to patients with clinical retrocochlear lesion impression in IAC and cerebellopontile angle, who present a clinical frame of unilateral or asymmetric neurosensorial deafness associated to tinnitus, vertigo and altered or not audiologic tests.

In grown up patients with initial high tone engagement and bilateral symmetric  hypoacusia NS, the first possible diagnosis is the Presbyacusia, but an overadded cause such as dolichoectasia of the basilar artery, compressive loops, acoustic trauma or other treatables causes such as an acoustic schwanoma must be dumped, more over if there is asymmetry in the hypoacusia or  deafness. In our series we did not find any case of retrocochlear tumoral lesion.
 
In acute deafness cases this study must also be used because up to 20% of the acoustic neuromas cases present this type of deafness. In our case we could visualize cochlear apex obliteration and partial obliteration of the posterior semicircular channel in the ear that is correlated with the clinic frame of sudden right deafness associated to vertigo and homolateral lateropulsion but we can not prove that it is not an accidental finding.
 
The visualization of the endolymphatic duct and sac is difficult, it was only visualized in 42.5% so it is impossible to correlate the non visualization  (53.8%) with the diagnosis of Meniére disease, as it has been stated by some authors (31). 
 
In our study, we obtained an excellent identification of the anatomic structures; we reported the cases in which we found  evident alterations in the 3DT2-TSE sequences using inframillimetric cuts, in agreement with those found in the literature, we introduced such sequences in the study of those patients having clinical suspicion of the membranous labyrinth, acoustic-facial nervous package and auditive via pathology.

It doesn’t exist, nor is this a study of the method sensitivity and specificity,  that would be ideal, but it is not possible to correlate surgically the findings in all the cases because they are not usually surgically treated and during an implant not all the described structures may be visualized. However, it is a very useful technique that in some occasions may be used alone but generally it must be part of a complete study of MRI including some other sequences such as the potentiated in T1 before and after the contrast, potenciated study in T2 of the encephalon, AMR, and even high resolution CT.

9. CONCLUSIONS

 
9.1      The 3D-MRI allows the visualization of the internal ear structures and also the detection of internal ear alterations that may be responsible for the deep NSH.
9.2             The high resolution computerized tomography with axial and coronal cuts, and the 3D-MRI are very important imagenologic studies in the diagnosis of deep NSH and we may not disqualify the computerized tomography because we consider that both studies are complementary.
9.3             In about 55% of the patients having idiopathic deep NSH, it was possible to determine some type of structural alteration of the internal ear or IAC that could explain the hypoacusis.
9.4             The expanded vestibular aqueduct syndrome is an etiology that must be considered in the diagnosis of the idiopathic deep NSH and the alteration might be detected by 3D-MRI.
9.5             In those patients having secondary deep NSH to meningitis it is feasible to detect, near 14%, membranous labyrinth obliteration.
9.6             It is necessary to gain more experience in the interpretation of the 3D-MRI with the objective of detecting some other pathologies that up to now are unknown.